In U.S. patent application Ser. No. 11/821,659, filed on Jun. 25, 2007 and entitled “Non-Fibrous High Modulus Ultra High Molecular Weight Polyethylene Tape for Ballistic Applications”, there was presented a non-fibrous, monolithic, ultra high molecular weight polyethylene tape product and a method for producing it. The non-fibrous UHMWPE tape was obtained by compression molding ultrahigh molecular weight polyethylene powder at a temperature below its melting point and then calendering and drawing and the resultant compression molded polyolefin at a total draw ratio of at least 100:1. A compression force of 25 kgf/cm2 was applied to compress the UHMWPE powder and the resultant sheet was calendered in a single calender nip and subsequently drawn under specific temperature and tension conditions to produce a high modulus tape.
Although the aforementioned patent application adequately provided a high modulus, high strength tape product for use as the high modulus component in ballistic-resistant products, the production rate was limited as a result of the high compression forces required in the compaction portion of the process. Compaction units are constructed of equipment that rises exponentially in cost as the throughput and operating pressure increases, including larger hydraulic cylinders, larger and longer rollers, and a larger framework to support the larger equipment. All of these pieces of equipment must be increased in size and strengthened significantly as the compaction pressure is increased. Therefore, to meet the required throughput in the production of high modulus UHMWPE tape, increasing the pressure on the compaction unit would require a significant investment in larger equipment.
What is needed therefore is a process for producing a high modulus, high strength component for use in ballistic-resistant articles that does not require compacting polyethylene particles at high pressure. The process should produce a high modulus product that includes the properties required for forming the shock-absorbing component in ballistic-resistant articles.